So, I installed dependencies and then attempted an install of BreezeBlurred from the AUR.
I can't figure out why the install failed. Here's where the error starts:

/home//.cache/yay/breeze-blurred-git/src/BreezeBlurred/breezebutton.cpp: In member function ‘void Breeze::Button::drawIcon(QPainter) const’:
/home//.cache/yay/breeze-blurred-git/src/BreezeBlurred/breezebutton.cpp:339:34: error: aggregate ‘QPainterPath path’ has incomplete type and cannot be defined
339 | QPainterPath path;
| ^~~~
/home//.cache/yay/breeze-blurred-git/src/BreezeBlurred/breezebutton.cpp: In member function ‘QColor Breeze::Button::backgroundColor() const’:
/home//.cache/yay/breeze-blurred-git/src/BreezeBlurred/breezebutton.cpp:404:35: warning: ‘T QWeakPointer::data() const [with T = KDecoration2::DecoratedClient]’ is deprecated: Use toStrongRef() instead, and data() on the returned QSharedPointer [-Wdeprecated-declarations]
404 | auto c = d->client().data();
| ^
In file included from /usr/include/qt/QtCore/qsharedpointer.h:48,
from /usr/include/qt/QtCore/qpointer.h:43,
from /usr/include/qt/QtCore/QPointer:1,
from /usr/include/KDecoration2/kdecoration2/decorationbutton.h:27,
from /usr/include/KDecoration2/KDecoration2/DecorationButton:1,
from /home//.cache/yay/breeze-blurred-git/src/BreezeBlurred/breezebutton.h:24,
from /home//.cache/yay/breeze-blurred-git/src/BreezeBlurred/breezebutton.cpp:21:
/usr/include/qt/QtCore/qsharedpointer_impl.h:565:8: note: declared here
565 | T *data() const noexcept { return internalData(); }
| ^~~~
make[2]: *** [CMakeFiles/breezeblurred.dir/build.make:120: CMakeFiles/breezeblurred.dir/breezebutton.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:404: CMakeFiles/breezeblurred.dir/all] Error 2
make: *** [Makefile:149: all] Error 2
==> ERROR: A failure occurred in package().
Aborting...
error making: breeze-blurred-git